net: cdc_ncm: add .ndo_set_rx_mode to cdc_ncm_netdev_ops

The cdc_ncm driver overrides the net_device_ops structure used by usbnet
to be able to hook into .ndo_change_mtu. However, the structure was
missing the .ndo_set_rx_mode field, preventing the driver from
hooking into usbnet's set_rx_mode. This patch adds the missing callback to
usbnet_set_rx_mode in net_device_ops.

Signed-off-by: Miguel Rodríguez Pérez <miguel@det.uvigo.gal>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>